Production of green and sustainable ultra-high-performance concrete using treated recycled fine aggregates

This study presents a sustainable and low-carbon approach for producing ultra-high-performance concrete (UHPC) by replacing natural fine aggregate with recycled fine aggregate (RFA) treated using waste-derived materials. Five RFA treatment methods were investigated: pressurized CO2 sequestration, silica fume (SF) slurry coating, volcanic ash (VA) slurry coating, and hybrid SF+CO2 and VA+CO2 treatments. Treated RFA was characterized using water absorption, density, specific gravity, XRD, and SEM-EDS analyses, while UHPC mixtures were evaluated for fresh, mechanical, and durability properties. The treatments significantly improved RFA quality, with the SF+CO2 hybrid method reducing water absorption by up to 38%. CO2-based treatments also enabled sequestration of approximately 3% CO2 by RFA weight. UHPC containing SF+CO2-treated RFA achieved a 28-day compressive strength slightly higher than conventional UHPC with NFA and 23% higher than UHPC with untreated RFA. Durability properties and resistance against drying shrinkage were also significantly improved, demonstrating the feasibility of producing high-performance green UHPC using RFA.